In recent years, various kinds of portable information processing devices have become common, tablet computers being typical examples of such devices. A tablet computer has a flat approximately rectangular solid case. The case accommodates a processing module, a control module, a communication module, and other elements. The case has one flat surface provided with a display panel (user interface section). The tablet computer is operated by touching the panel. However, to improve convenience, a separate human interface device can be attached to the tablet computer when needed. For example, a keyboard can be connected by a cable or wirelessly to make character input, etc., easy.
A tablet computer and a keyboard are separate from each other, but they can be connected with each other whenever necessary, thereby improving convenience. However, the tablet computer and the keyboard must be carried separately, which may be awkward. To improve portability, it is possible to use a case which accommodates both the tablet computer and the keyboard. However, it is then necessary for the user to walk around with a case in addition to the tablet computer and the keyboard, and this may be inconvenient. To cope with this problem, it is possible to use a hinge mechanism whereby the tablet computer supports the keyboard in the way a clamshell notebook computer does. However, it is then necessary to additionally provide a separate hinge mechanism, which may make the entire system bulky. The addition of a separate hinge mechanism is not desirable from the point of view of slimming down the tablet computer or the keyboard.